The present invention relates generally to resonant power converters and, more particularly, to a series resonant converter controlled to operate in a super-resonant switching mode in order to achieve zero-voltage switching under all operating conditions.
Classical optimal control involves operating a full-bridge switching converter in a full square wave mode of operation. That is, both diagonal pairs of switching devices are switched on and off simultaneously. Unfortunately, classical optimal control results in higher than desirable switching losses and less than desirable dynamic performance for some applications. For example, for x-ray generation, classical optimal control does not meet strict performance criteria. Such criteria include the following: a fast generator voltage rise time in order to avoid an excess radiation dose to patients; minimal generator voltage ripple in order to avoid imaging jitter problems; avoidance of voltage overshoots which would create an additional radiation dose to patients; high audiosusceptibility, or line voltage ripple rejection, to avoid jitter and to ensure a tightly regulated output; independence of generator with respect to line voltage variations for consistent imaging performance; maintenance of a constant output voltage for high-quality successive images; reduction of high frequency currents flowing from the power converter back into the dc bus capacitors; and compliance with electromagnetic interference regulations.
Accordingly, it is desirable to provide a control for a series resonant converter which results in a very fast response time while maintaining zero-voltage switching operation. It is furthermore desirable that such a control meet strict performance criteria such as those set forth hereinabove.